The present invention relates to a method for producing a cutter, and more particularly to a method for welding cutter segments composed of sintered compacts, which comprise diamond or CBN (cubic boron nitride) grit, to a core body.
FIG. 1 shows a conventional method of fixing cutter-segments that contain diamonds onto a core body. A circular blade as shown is mounted on a motor-driven shaft (not shown) by, for example, use of a center hole 2a and is used as a handy cutter, for such operations as (1) cutting bricks, slates and tiles, (2) trimming stone blocks, (3) cutting iron sheets, concrete pipes and concrete blocks, (4) grooving concrete roads, (5) forming curved surfaces on stone blocks, (6) chamfering stone blocks and (7) beveling stone blocks.
In FIG. 1, the numeral 2 denotes a steel core, and the numeral 1 is a cutter segment made of a mixture of bond powder, such as Co (cobalt), and diamond or CBN grit, which has been compacted and sintered (in most cases, by hot pressing) to nearly 100% apparent density. Such segments are fixed onto the core 2 by brazing to make a cutter blade.
The multi-segment circular cutter made by the above conventional process has defects and problems as described below:
(a) When this kind of brazed blade is used under such severe conditions, such as cutting without a lubricant like water (dry condition) along with uneven loading on segments, a concentration of heat at a specific segment can be observed. The heat concentration results in the softening of the solder and consequently tends to result in accidents from detachment of the segment.
(b) In the case of the brazing process, a high-frequency electric device or gas burner used as a means of heating will heat not only the brazing boundary but also a large area of the adjacent core 2, causing a metallographic structural change there which induces distortion of the core. This problem, which, in general, is common to the brazing of multi-segment tools made of a circular iron core, becomes particularly serious in the case of small diameter cores such as those for handy or wagon-type portable diamond cutters, because the ratio of heat-affected zone to the total area of the core is fairly large and the ratio of thickness to the diameter of the core is fairly small. In order to prevent this distortion, slots 3 as shown in FIG. 1 are provided to release the local strain and to prevent heat conduction from one segment to the next during the brazing process. It is a commonly-held view of the diamond blade industry that the core for the above-mentioned portable diamond cutter should by all means be provided with slots. These slots, however, result in the disadvantage of weakness of the core design against static or dynamic loads on the core.
(c) Heating during the brazing process induces the phenomenon of annealing of the material in a large area of the core 2, which causes degeneration of the resistance of the core against bending stress.
With regard to FIG. 2, generally speaking, in all cases of the welding process or the brazing process, the necessary condition for achieving high joining strength is to avoid weakening the structure at any heat-affected zone Y of the segment, metallic joining layer like solder X or heat-affected zone Z of the core.
Above-mentioned explanation (a) relates to layer X, and explanation (c) relates to layer Z. Problems (a) and (c) are inherent to the brazing process and problem (b) is inevitable in the case of a high-frequency heating process.